Performance Of SiC Radiation Detector And Its Degradation

Radiation detection technology is of great significance in many fields such as nuclear medicine,nuclear power plant monitoring,environmental monitoring,space physics,particle physics and industrial application.Compared with conventional gas chamber and scintillator detector,detectors made from semiconductor such as silicon and/or germanium gain more and more popularity with advantages of high efficiency,large linear response range,short response time,compact size,simple structure,high detection efficiency and excellent energy resolution.With the expansion of application scope,conventional semiconductor detectors do not have the capability to deal with the increasingly harsh environment with high temperature and/or high irradiation intensity as silicon and germanium are both narrow band-gap semiconductor,with poor radiation resistance and low stability against high temperature.Thus,new semiconductor materials are required.For the past decades,Silicon Carbide?SiC?has been be recognized as one of the key materials for high power devices due to its superior material properties over conventional semiconductors.The properties of wide band gap,high breakdown field,large carrier saturation velocity,excellent thermal conductivity and high displacement threshold energy also make SiC a highly suitable material for radiation detection at room temperature and above.In the present work,PIN detectors have been fabricated from high quality n-type 4H-SiC epitaxial layer grown on n-type 4H-SiC bulk substrate to investigate the performance and the degradation of SiC detector.Radiation damage of these devices has been carried out by a neutron fluence of 1×10¹⁵cm^-2.Current-voltage?I-V?and capacitance-voltage?C-V?are measured before and after neutron irradiation.DLTS analysis were carried out to find the Z1/2 defect concentration,which would be a key parameter to characterize the degradation.Spectra of 5.48 MeV?particles from a ²⁴¹Am source have been used to quantitatively characterize the degradation of the devices.14.1 MeV neutron and X-ray have also been used to investigate the performance of the detector.To quantitatively analyze the experimental results,an improved method to calculate pulse-height spectra has been adopted rather than the commonly used energy deposition spectrum.Current pulses of the detector were firstly calculated using TCAD.With the help of Multisim,pulse-height of the output voltage were then carried out.After the determination of energy-angle distribution of incidence particles,pulse-height spectra were finally carried out using a monte-carlo method.The state-of-art on SiC is given in chapter 1.Chapter 2 describes the principle of semiconductor detector and detection system.The basic principle of pulse-height spectra calculation is discusses in chapter 3.Two examples are given to make a comparison between our calculation results and the reported experimental results.Calculation results show good agreement with the experimental one and a new explanation of the observation of 2 peaks in the spectra is given.Chapter 4 illustrates the details of device design and fabrication.Detection performance of 5.48 MeV?particles,14.1 MeV neutrons and 60⁷0keV X-ray using our detectors are given in chapter 5.Spectra of 5.48 MeV?particles are given,both the experimental one and the calculated one,and our improved method shows an excellent approximation to the experimental results.Spectra of 14.1 MeV neutron shows almost the same shape as other reported results.The main characteristic peak related to ¹²C?n,??⁹Be owns an FWHM of 2.4%,which is only a bit worse than the best result of2.2%ever reported.The time performance of X-ray detection is not good enough as but close to a commercial Si-PIN detector.To quantitatively analyze the degradation of detectors,a two-independent levels model to describe Z1/2 defect in TCAD were adopt and examined by other reported results.Concentration of Z1/2 defect after irradiation were found out using DLTS.With the new model,shift of ²⁴¹Am spectra with different bias voltage was calculated before and after neutron irradiation.Our simulation results of CCE show an acceptable agreement with the experimental results.